Dietary arginine supplements have been shown to have beneficial effects on the immune system, wound healing, recovery from surgery. However, the effects on cancer are inconsistent. Although arginine has been reported to inhibit tumor growth in some studies in cell cultures and animal models, in other studies, including work on human patients, a stimulation of tumor growth has been reported. The hypothesis of this proposal is that the ability of arginine supplements to stimulate tumor protein synthesis and cell proliferation in humans may be limited to specific types of cancer. Arginine supplements might therefore be used to advantage in some cancer patients to improve recovery from surgery, immunity and wound healing, without the risk of stimulating the tumor or remaining metastases. The aim is therefore to investigate how dietary arginine supplements (30g/d for 3 days) influence protein synthesis and in the expression of cell proliferation markers in a range or proliferative and non-proliferative healthy tissues and in malignant and benign tumors of surgical patients.